Evaporators-condensers



Feb. 4, 1958 C. BARBARESCHI EVAPORATORS-CONDENSERS 2 Sheets-Sheet 1 Filed Sept. 11, 1952 Feb. 4, 1958 c. BARBARESCHI EVAPORATORS-CONDENSERS Filed Sept. 11, 1952 2 Sheets-Sheet 2 FIG. 3

- INVENTOR. I 710 BIPBflFZ S 1 United States Patent EVAPORATORS-CONDENSERS Carlo -Barbareschi,Milan, Italy Application September 11, 1952, Serial No. 308,994

Claims priority, application Italy (October 18, 1951 11 Claims. (Cl. 159-11) This invention relates to evaporators, and more particularly to evaporators employing a heated element to process a liquid.

In evaporation processes, for instance, for the distillation of sea water or for the concentration of chemical or alimentary solutions, wherein the formation of deposits over the heated surfaces of the evaporator results in,

periodic suspensions of service are required for cleaning to maintain an efficient transmission of 'heat.

A loss in heat transmission efiiciency becomes particularly serious when the evaporating system makes it necessary to work with a small difference of temperature between the heating element and the liquid to be evaporated, as in the case of the application of a thermo-compression cycle or in the case of the utilization of exhaust steam at low pressure as the heating fluid.

Accordingly, it is an object of the present invention to provide an improved evaporator in which efliciency is maintained substantially constant.

One embodiment of the invention is characterized by the provision of a heat exchange surface in an evaporating chamber containing the liquid to be evaporated. The liquid to be treated evaporates on the heat exchange surface and a rotating means is provided which not only supplies the liquid to the surface, but also maintains the surface substantially free from deposits.

The invention and its objects are further illustrated by way of example in the accompanying drawings, in which:

Fig. l is a longitudinal section of an evaporator-condenser according to the invention, including in this instance three heat exchange boxes;

Fig. 2 is a cross section of the same apparatus on line 22 of Fig. 1, with the heat exchange boxes seen from the side;

Fig. 3 shows one of the heat exchange boxes in a longitudinal section;

Fig. 4 is an enlarged view of a cross section of this box according to line 4-4 of Fig. 3; and

Fig. 5 shows perspectively one of the mechanical cleaners.

In these drawings, 1 indicates the heat exchange boxes that are fixed side by side in evenly spaced relationship to the lower part 13 of a sealed evaporating chamber composed of two half chambers, the upper part being indicated by reference character 14. The interior of each box is combined for the accomplishment of its task with pipes, which extend out of the apparatus by means of an air tight passage through the lower part 13 of the evaporating chamber. The upper part 14 acts only as a cover that can be applied over a previously assembled unit.

The steam enters through conduit 2 into a header 3 where it passes into the inlets 4 of the several boxes, the latter working thus in parallel.

In said boxes, the steam travels upwardly through zigzag passages formed by channel-shaped bands 7, and during this travel, which causes its condensation, this steam causes the evaporation of the liquid which is in contact with the outer surfaces of said boxes.

2,822,039 Patented Feb. 4, 1958 in a direction opposite to that of the steam, run down to the bottom of the box, wherefrom it discharges to the exterior through a pipe 5. Thus the condensate is prevented from streaming down vertically along the inner walls of the boxes and preventing the regular transmission of heat.

On the other hand channels 7 are disposed in spaced relationship at progressively diminishing distances so that the passage area for the steam becomes gradually smaller as the steam condenses to maintain its speed constant. At the upper end of the 'box accumulates the uncondensed gases which are left after the condensation of the steam, said gases discharging to the outside through pipe 6.

Finally, the channel-shaped bands 7 serve to connect the two longitudinal plane surfaces of the box in order to increase their resistance against the pressure exerted by the steam.

Boxes 1 have, in convenient positions, holes 8 for accommodating shafts- 9 that are supported and driven from the outside andto which paddles 10 (Fig. 5) of the cleaners are firmly fixed. According to the areas of the longitudinal walls of the boxes, it will be possible to dispose over one of said walls any desired number of cleaners.

Said cleaners (two foreach wall in the example shown) are disposed parallel to the longitudinal plane surfaces of the boxes. Paddles 10, tapering towards their extremities, are provided with a sheath 11, readily removable, to which are fixed flexible metal blades 12 that during the rotation scrape the surfaces of the boxes, preventing thus the formation of scale deposits. These blades are disposed over a single side of sheath 11 in the cleaners intended to work over a single face of a box and over both sides of the sheath in the cleaners interposed between two contiguous boxes. 7

Through a very exact construction of the cleaners a rubbing of the blades over the surface of the boxes can be avoided to allow these surfaces to cover themselves initially with a slight scale layer which cannot further grow on account of the action of the cleaners.

Paddles 10 of the cleaners are fixed to shaft 9 with a relative angular displacement to obtain a succession of immersions of the cleaners in the liquid, this having the effect of dividing the resistances to rotation of these elements.

The arrangement of the cleaners together with the selection of a convenient speed of rotation make .it possible to realize a lifting of the liquid to be evaporated which has as an effect that the whole surface of each box is constantly wiped with the liquid in the event that it is desired to support the boxes only partially in the mass of the liquid to be evaporated.

In fact, it is to be noted that according to the nature of the liquid to be treated, its density and viscosity, its tendency to foam, its boiling point and the temperature fall by which the transmission of heat is to be obtained, it may be convenient to effect the evaporation by leaving the faces of the boxes totally or partially free from the liquid to be evaporated or else by keeping said boxes Wholly immersed in the liquid.

Should it be preferred to realize the evaporation with the box surfaces entirely free, that is by keeping the boxes above the level of the liquid to be evaporated, it will be possible by means of a pump 19 to lift the liquid above said boxes so as to cause its distribution by letting it overflow from channels. The result is that the liquid,

falling from said channels, will cover the surfaces of the boxes with a thin layer of liquid. The very structure of the boxes provides at the upper part, as shown in Fig. 4, a channel that can be used to this end.

The liquid to be evaporated enters the evaporating chamber through conduit 16, the concentrate discharges through 17. The evaporated portion leaves through conduit 18 from the upper part 14 of the evaporating chamher and may be sent into a condenser or sucked out v the static pressure determined by the head of the liquid and render it possible to conveniently replace by said mechanical action the limited influence of the convection of the liquid in the transmission of heat.

Under these conditions, the apparatus provided by the invention permits the condensation of the steam in the interior of the boxes and the evaporation of the liquid to be treated on the outside even with very small differences of temperature, so that it is suitable for the thermo-compression cycles and for the utilization of low pressure exhaust steam.

The details of the apparatus may be varied without departing from the scope of the invention. Thus, for instance, the metal blades of the cleaners can be replaced by metal brushes mounted on the paddles of these cleaners and rubber bands or other analogous devices can be applied on said paddles.

On the other hand, it is to be noted that the apparatus may in some cases be so disposed as to have an arrangernent differing from that indicated in the preceding description. More particularly, to separate vapors from the solutions in which they originate, the interior of the apparatus may be made to work as a distilling column so that through the outlet opening provided for uncondensed gases may discharge a mixture of steam and of vapors coming from the solution subjected to concentration. For instance, by so concentrating the bisulphite solutions coming from the fabrication of wood cellulose, it is possible to extract a certain quantity of furfural.

What I claim is:

1. An evaporator comprising in combination: a casing having an inlet for the supply of liquid to be evaporated, a first outlet for the discharge of concentrated liquid, and a second outlet for the discharge of gaseous medium generated during evaporation, a pluralityof substantially plane, vertical heating plates arranged inside said casing with substantial areas for contact with said liquid to be evaporated, said heating plates being substantially parallel to each other and extending from adjacent the bottom of said casing to positions spaced from the top of said casing, means for heating said heating plates, and rotatable means rotatably arranged within said casing for rotation around a substantially horizontal axis, said rotatable means being in contacting relationship with said heating plates for lifting said liquid in said casing and wiping the same against said heating plates and for preventing the growth of deposits on the latter.

2. in an evaporator as claimed in claim 1, said inlet and said first outlet being in the lower portion of said casing, and said second outlet being in the upper portion of said casing.

3. In an evaporator as claimed in claim 1, said casing being tightly closed and having openings only at said inlet and said outlets.

4. An evaporator comprising in combination: a casing having an inlet for the supply of liquid to be evaporated,

a first outlet for the discharge of concentrated liquid, and a second outlet for the discharge of gaseous medium generated during evaporation, a plurality of substantially plane, vertical heating plates arranged inside said casing for contact with said liquid to be evaporated, said heating plates being substantially parallel to each other, means for heating said heating plates, and rotatable means rotatably arranged within said casing for rotation around a substantially horizontal axis, said rotatable means being in close relationship to said heating plates for lifting said liquid in said casing and bringing same into contact with said heating plates and for preventing the growth of deposits on the latter, said inlet and first outlet being in the lower portion of said casing, and said second outlet being in the upper portion of said casing, said casing being tightly closed and having openings only at said inlet and said outlets, said rotatable means including a rotatable substantially horizontal shaft journalled in said casing, said heating plates having bores through which said shaft passes, at least one radially extending paddle rigidly connected with said shaft, and a plurality of blades mounted on said paddle in a row, the free ends of said blades being in close proximity to said heating surface.

5. In an evaporator as claimed in claim 4, said blades being made of a flexible metal.

6. An evaporator comprising in combination: a casing having an inlet for the supply of liquid to be evaporated, a first outlet for the discharge of concentrated liquid, and a second outlet for the discharge of gaseous medium generated during evaporation, a plurality of substantially plane, vertical heating plates arranged inside said casing for contact with said liquid to be evaporated, said heating plates being substantially parallel to each other, means for heating said heating plates, and rotatable means rotatably arranged within said casing for rotation around a substantially horizontal axis, said rotatable means being in close relationship to said heating plates for lifting said liquid in said casing and bringing same into contact with said heating plates and for preventing the growth of deposits on the latter, said inlet and first outlet being in the lower portion of said casing, and said second outlet being in the upper portion of said casing, said casing being tightly closed and having openings only at said inlet and said outlets, said rotatable means including a rotatable substantially horizontal shaft journalled in said casing, said heating plates having bores through which said shaft passes, at least one radially extending paddle rigidly conected with said shaft, a sheath covering said paddle and mounted thereon, and a plurality of blades mounted on said sheath in a row, the free ends of said blades being in close proximity to said heating surface.-

7. An evaporator comprising in combination: a casing having an inlet for the supply of liquid to be evaporated, a first outlet for the discharge of concentrated liquid, and a second outlet for the discharge of gaseous medium generated during evaporation, at least one heating unit inside said casing and positioned as a whole towards the bottom of the casing, said heating unit being in the shape of a closed box having a pair of substantially vertical side Walls, said side walls being arranged for contact with the liquid to be evaporated, said box having an intake opening for a heating medium, a first discharge opening for the condensate of said heating medium, and a second discharge opening for a gaseous medium generated during condensation of said heating medium, and at least one rotatable member rotatably arranged within said casing adjacent to a side wall of said heating unit for rotation around a substantially horizontal axis, said rotatable memher being in its entirety in close relation to said heating unit for lifting said liquid in said casing and bringing same into contact with said side wall of the heating unit and for preventing the growth of deposits on the latter.

8. in an evaporator as claimed in claim 7, said intake opening of the box and said first discharge opening of the box being'at the lower portion of said box, and guiding means inside said box for guiding the condensate from an upper portion of the box to said first discharge opening, so that the heating medium and the condensate thereof travel in opposite directions.

9. In an evaporator as claimed in claim 8, said guiding means including a plurality of strips extending longitudinally of said box, each strip having a V-shaped crosssection with a depression substantially in the center between the side walls of the box for collecting the condensate and keeping same away from the side walls.

10. In an evaporator as claimed in claim 8, said guiding means being in the shape of superposed strips extending from one end of the box almost to the other end thereof, the distance between the superposed strips decreasing from the bottom to the top so as to provide for a substantially constant speed of the heating medium from the bottom to the top while it condensates.

11. An evaporator comprising in combination: a casing having an inlet for the supply of liquid to be evaporated, a first outlet for the discharge of concentrated liquid, and a second outlet for the discharge of gaseous medium generated during evaporation, at least one heating unit inside said casing, said heating unit being in the shape of a closed box having a pair of substantially vertical side Walls, said side Walls being arranged for contact with the liquid to he evaporated, said box having an intake opening for a heating medium, a first discharge opening for the condensate of said heating medium, and a second discharge opening for a gaseous medium generated during condensation of said heating medium, and at least one rotatable member rotatably arranged within said casing adjacent to a side wall of said heating unit for rotation around a substantially horizontal axis, said rotatable member being in close relation to said heating unit for lifting said liquid in said casing and bringing the same into contact with said side wall of the heating unit and for preventing the growth of deposits on the latter, said intake opening of the box and said first discharge opening of the box being at the lower portion of said box, and guiding means inside said box for guiding the condensate from an upper portion of the box to said first discharge opening, so that the heating medium and the condensate thereof travel in opposite directions, said guiding means including a plurality of superposed channel-shaped strips extending longitudinally of said box, each strip having a depression substantially in the center between the side walls of the box for collecting the condensate and keeping same away from the side walls.

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